JPH0443406B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a projection exposure apparatus, and more particularly, to a projection exposure apparatus suitable for manufacturing highly integrated semiconductor devices.

[Background of the invention]

An example of a conventional projection exposure apparatus is shown in FIG. In the figure, there is an XY stage 1 on which a wafer 2 to be exposed is placed, and this XY stage 1
is step-and-repeat in the X and Y directions by drive motors 3 and 4. The position control of this XY stage 1 is performed by a laser length measurement system 5, and its accuracy reaches about 0.05 μm. XY
Above the stage 1, from top to bottom, there are, in order from top to bottom, an exposure illumination system 6, a condenser lens 7, and a reticle 9, which is an original image placed on a reticle mounting table 10.
and a reduction lens 8 are arranged, and the reticle 9
The image is projected onto the two surfaces of the wafer. In addition, the pattern detectors 11 and 12
are arranged, and these pattern detection systems 11 and 12 are
An image obtained by passing the detection pattern 13 on the two wafer surfaces through the reduction lens 8 and the square hole pattern 14 formed in the reticle 9 is transferred to the mirror 11d,
12d, half mirror 11c, 12c, lens 1
1e, 12e and pattern detectors 11b, 12b obtained through slits 11f, 12f. Note that the half mirror 11
c, 12c are irradiated with light from detection illumination units 11a, 12a. To perform projection exposure using such an apparatus, the wafer 2 is placed on the XY stage 1, the first reticle 9 is placed on the original plate 10, and then the exposure illumination system 6
The light generated by and condensed through the condenser lens 7 passes through the reticle 9 and passes through the reduction lens 8.
In order to accurately overlay and transfer the pattern of the reticle 9 onto the wafer 2 on the XY stage 1, the monochromatic light from the detection illumination units 11a and 12a is transmitted to half mirrors 11c and 12, respectively.
c, reduction lens 8 from square hole pattern 14 provided on reticle 9 via mirrors 11d and 12d;
irradiate the wafer 2 through the wafer 2, form an image of the detection pattern 13 on the wafer 2 on the reticle 9,
Each enlarged image is shown on the mirror 11.
d, 12d, and half mirrors 11c, 12c to pattern detectors 11b, 12b. From this measurement, the relative error between the positions of the wafer 2 and the reticle 9 is known, and this relative error is fed back to the control of the XY stage 1 to perform transfer.

Here, the pattern detection system will be described in more detail using FIG. 2. Figure 2 shows the X shown in Figure 1.
Axis pattern detection system 11 and Y-axis pattern detection system 12
For the purpose of simplifying the explanation, X-axis pattern detection system 11
Only the following are shown. First, the detection light illumination section 11a
The output detection light passes through the half mirror 11c and the square hole pattern 14 of the reticle 9, passes through the reduction lens 8, and illuminates the detection pattern 13 on the wafer 2.
The reflected image thus obtained is back-projected by the reduction lens 8 and formed on the square hole pattern 14 of the reticle 9. Reference numeral 15 in the figure indicates this imaging state. This image is passed through the slit 11 by the lens 11e.
The image is formed on f. By scanning this image with the slit 11f, the photomultiplier 11g detects the light intensity at each position of the slit. This data is A/D converted by the A/D converter 15 and taken into the CPU 16. In this way, the distribution of reflected light from the detection pattern 13 on the wafer 2 is detected as a waveform such as 17 shown in the figure. At this time, ΔX shown in FIG. 17 is the distance between the center of the square hole pattern 14 of the reticle 9 and the center of the image of the detection pattern 13 of the wafer 2, and this amount is expressed as the relative deviation amount between the wafer and the reticle. By correcting this during the exposure step, the wafer and reticle can be accurately aligned. Conventionally, in the projection exposure apparatus configured in this manner, the detection pattern 13 formed on the two surfaces of the wafer is formed as a concave or convex pattern, and the concave (or convex) pattern is detected. Further, the projection exposure apparatus generally uses a lens dedicated to monochromatic light in order to improve the resolution of exposure.
Therefore, in the through-the-lens detection method as described above, even if the light from the detection illumination section 11a is mixed with light of other wavelengths instead of monochromatic light, the reduction lens 8
Due to the chromatic aberration, defocus occurs in the pattern detection section 13, and the resulting detected waveform is almost the same as that of monochromatic light. Now, in the manufacture of semiconductor devices, the wafer 2 is usually coated with a photosensitive agent called photoresist to a thickness of about 1 μm. A transparent film, such as photoresist, on the wafer 2 that is as thin as the wavelength of light is called an optical thin film, and can be shown in the model of FIG. The reflected light of the detection light includes reflected light 21 from the surface of the photoresist 25, reflected light 22 from the wafer 2, and after reflection from the wafer 2,
The light reflected on the surface of the photoresist 25 and the light reflected on the wafer 2 is classified into multiple reflected light 23, and these lights interfere with each other.

Now, let the incident light intensity be 1, and the refractive index of air be n,
When the refractive index of the resist is n _p , the refractive index of the substrate is n _g , the wavelength is λ, and the resist thickness is t, the reflected light intensity E _p
is the following formula (1) E _p = 1-4n _p n ² n _g /n ² (n _p + n _g ) ² − (n _g ² − ^{n 2} )
(n ² −n ² _p ) sin (δ/2)……(1) However, it is expressed as = δ = 4nπt/λ. Reflected light intensity without resist
By substituting t=0, E _p becomes E ₀ ={(n _p −n _g )/n _p +n _g )} ² .

Also, in Figures 4 and 5, n=1, ng=4.86, n
= 1.67 and shows how the relative reflection intensity based on E _p changes with respect to the resist film thickness. Figure 4 shows the G line of λ = 4160 (Å),
FIG. 5 shows the case where E-line with λ=5460 (Å) is used as the detection light. As shown in FIGS. 4 and 5, it can be seen that when a difference in film thickness occurs, the intensity of reflected light changes.

Normally, in the LSI manufacturing process, wafer 2
Detection patterns with various step structures are formed thereon. Since the depth of a step is mainly determined by performance factors of the LSI, a projection exposure apparatus used as a manufacturing device is required to have stable detection ability for detection patterns of various step structures. Conventionally, the most difficult pattern to stably detect is a detection pattern with small steps. FIGS. 6a and 6b each show a cross-sectional view of a detection pattern with a typical low-step structure. In the figure, 51 is a silicon substrate, 52 is SiO ₂ , and 53 is a silicon substrate.
Si ₃ N ₄ , 54 is a photoresist. Such a detection pattern is illuminated with monochromatic light, back-projected onto the hole on the reticle 9 by the reduction lens 8, and further imaged on the slit 11f. The light intensity distribution of the image is usually as follows.
The result will be as shown in Figure 7. Figure 7 is 17 in Figure 2.
Although the waveform has the same meaning as the waveform shown in , the image of the edge portion 31 of the detection pattern is not clearly displayed due to the low step difference, and as explained above, reflection due to the difference in photoresist film thickness between the detection pattern portion and the peripheral portion. A signal based only on the difference in light intensity can be obtained.

As shown in Fig. 8, the difference between the photoresist film thickness t _c in the pattern area and the photoresist film thickness t _p in the peripheral area can be determined by experiment, t _c −t _p = ad (−0.2 μm<d<0.2 μm) It has been confirmed that the following relationship (2) is satisfied. Here, a is the type of photoresist, the surface condition of the substrate,
It is a constant determined by the coating method and is usually around 0.6. In FIG. 8, 41 is a photoresist and 42 is a silicon substrate. Further, d is the step depth. Figure 9 shows the photoresist film thickness and relative reflected light intensity when using the same G-line detection light as in Figure 4. When the relationship between the thicknesses t _p and t _c is such that t _p +t _c =Nλ/2n・N=0, 1, 2..., the light intensity distribution of the image formed on the slit 11f is between the t c part and the t _c part. Since the relative reflection intensities at _{the p} part were equal, the waveform as shown in FIG. 9 was formed, which sometimes made detection difficult. There are countless combinations of t _p and t _c having such a relationship within the range of film thickness corresponding to one interference period of the detection light. As mentioned above, in conventional detection, the coating film thickness t _p and the pattern step difference d
Under certain conditions, there is no difference in the reflection intensity between the t _p part and the t _c part, and the detection pattern with a low step difference becomes difficult to detect because the dark part of the edge is difficult to be clearly projected as an image. It was hot.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a projection exposure apparatus that can accurately detect an object to be exposed having a detection pattern with a low level difference.

[Summary of the invention]

In order to achieve such an objective, the present invention
An original image of a fine pattern, an exposed object having a target pattern, a lens located between the exposed object and the original image for projecting the original image onto the exposed object, and a lens for detecting the target pattern through the lens. In a projection exposure apparatus that is configured with a pattern detector and that detects an image using monochromatic light during the detection, detects a concave pattern and a convex pattern provided in advance on the object to be exposed, and detects the detected waveform. The component having the larger gain is automatically selected, and the relative position of the exposed object and the original image is detected based on the data of the selected waveform.

[Embodiments of the invention]

FIG. 10 is an explanatory diagram showing an embodiment of the projection exposure apparatus according to the present invention, and is a diagram showing the configuration of a detection pattern on a semiconductor wafer used. In the same figure,
The detection pattern is composed of a convex pattern 61 and a concave pattern 62 that are adjacent to each other. In the convex pattern 61 and the concave pattern 62, the respective absolute values of the step differences d _t and d _p are equal. These absolute values do not have to be equal, but generally when forming each pattern by photolithography,
Since they go through the same process, they are usually equal.

When performing projection exposure using such a wafer having two detection patterns, as shown in the processing procedure of FIG. 11, the concave pattern is first detected to obtain a detection waveform X _p (1). Next, the convex pattern is detected and a detected waveform X _T () is obtained. Bypass processing is performed on these two waveforms. The bypass processing is a waveform processing performed to remove waveform inclinations and large undulations, and is described below.

X _ph ()=X _pa ()−X _pb () where X _pa () =X _p (−1)+X _p ()+X _p (+1)/3 Also, X _Th ()=X _Ta ()−X _Tb () However, X _Ta () =X _p (−1)+X _p ()+X _p (+1)/3 In this way, the bypass processing waveform X _ph (),
You can get X _Th (). Here, is the horizontal axis of the waveform, and in this example, indicates the position coordinates of the slit 11f. Next, calculate the maximum value minus the minimum value for each of X _ph () and X _Th () obtained in this way.

In other words, find maxX _ph () - minX _ph () = OG maxX _Th () - minX _Th () = TG and compare the sizes of OG and TG.

If OG>TG, the detected waveform is X _p
() is adopted, and if OG<TG, X _T () is adopted as the detected waveform.

In this way, it is possible to automatically select whichever of the concave and convex detection patterns is easier to detect.

Next, it will be explained below that in a concave or convex pattern, when either waveform component OG or TG is close to 0 and becomes difficult to detect, one of them does not become 0. In FIG. 12, t _p in FIG. 11,
The relationship between the film thickness of t _cp and t _cT and the relative reflected light intensity in G-ray detection is shown. From the above formula (2) t _c - t _p = ad (-0.2 μm < d < 0.2), a = 0.6
Assuming that, t _cT becomes the film thickness in FIG. 12, which is E(t _p )-E(t _cp )0, but it can be seen that E(t _p )-E(t _cT )≠0.

The conditions for E(t _p )−E(t _cp )0 and E(t _p )−E(t _cT )0 are such that the coating film thickness t _p is t _p =Nλ/4n+λ/8n N=0,1 , 2... and the detection pattern step satisfies 0.6d=λ/4n, and the combination of t _p and t _c that satisfies these two conditions is one interference period of the detection light. It can be seen that there is only one film in the range of film thickness corresponding to , and the probability of satisfying such a condition is extremely small.

〔Effect of the invention〕

As explained in detail above, a projection exposure apparatus has the function of setting a concavo-convex pattern as a detection pattern, sequentially detecting the concavo-convex pattern, comparing the sizes of the waveform components, and adopting the larger detected waveform as the waveform for superimposition. , it is almost always possible to detect wafers that have a detection pattern with a low level difference.

[Brief explanation of drawings]

Figure 1 is a diagram showing the configuration of a projection exposure apparatus, Figure 2 is a schematic configuration diagram for aligning a reticle with a wafer in a conventional projection exposure apparatus, and Figures 3 to 5 are the projection exposure apparatus. FIGS. 6a and 6b are cross-sectional views showing detection patterns on a wafer in a conventional projection exposure apparatus, and FIGS. FIG. 10 is a sectional view showing an example of a detection pattern on a wafer in the projection exposure apparatus according to the present invention, and FIG. 11 is a flowchart showing the processing procedure in the projection exposure apparatus according to the present invention. 12 are graphs showing the effects of the projection exposure apparatus according to the present invention. 1... Stage, 2... Wafer, 3, 4...
Drive unit, 5... Laser length measuring machine, 6... Exposure illumination system, 7... Condenser lens, 8... Lens, 9
... Reticle, 10 ... Original plate (reticle) mounting table, 11, 12 ... Pattern detection system, 13 ... Detection pattern on wafer, 17 ... Detection waveform example,
25,54,41...Photoresist, 2,51,
42...Si substrate.

Claims (1)

[Claims] 1. An original image of a fine pattern, an exposed object having a target pattern, a lens located between the exposed object and the original image for projecting the original image onto the exposed object, and detecting the target pattern through the lens. A projection exposure apparatus is provided with a pattern detection means for detecting a concave pattern and a convex pattern provided in advance on the exposed object in a projection exposure apparatus that obtains and detects an image using monochromatic light during the detection. The method is characterized in that the one having a larger gain of the waveform component of the detected waveform is automatically selected, and the relative position of the exposed object and the original image is detected based on the data of the selected waveform. Projection exposure equipment.